The plane is scorpio F5B, motor is hacker FAI (B40-6L), ESC is hacker master 105 opto.. prop is graupner 16x10... battery is 10 cell CP-2400.. It happened again today, coming out of a highspeed dive, the prop began to windmill.. The Brake arms properly each time and I've not noticed any radio glitching.. throttle trim verified at zero... Today it almost cost me the plane as it was a very fast dive and when the prop came unfolded and started windmilling the scorpio tucked badly... When I blip the throttle (start the motor) the prop will again fold normally... Does anyone have any ideas???.... For the next time out, I have switched to a RF 15x13 prop and tightened the prop pivot bolts a little tighter so there is some friction there, hoping this will help keep them folded where they belong!.

There are people here better qualified than I, but I'm guessing that one blade is partially unfolding as the airspeed drops. The airstream hits it, causes the prop to start turning, and then the second blade unfolds. Centrifugal force does the rest!

I read somewhere of a flier using small elastic bands to hold the blades folded. Applying the throttle opened the blades as normal.

Wrap a rubber band over one blade, back behind the spinner and over the other blade. A large periodontist's rubber band like a #6or #8 or a small, like a 1" commercial rubber band ( I don't remember the # ) works well. Put a couple of twists in it as it goes around the shaft or file some small notches in the back of the spinner to keep the rubber band from slipping.

Originally posted by tic ...... coming out of a highspeed dive,........

So this is not a slow speed thing. It sounds to me like the high speed is getting some air in behind the blades and then once they lift out a short ways from the model then they start to windmill.

The little rubber bands may help but then again they may not be enough unless you use a bunch and then the blades may not want to unfold cleanly when you want. This is certainly worth a try though. If it fixes the problem it's easy and cheap.

Brake? I gather this is an electric brake in the ESC? If so then you need to realize that it's only really effective when the motor is turning over at a fair number of rpms. It's the back EMF from the self generating of the permanent magnet motor being short circuited that damps out the rotations. These aren't really brakes in the true sense of the word. So given that the motor can start to windmill even with a folded prop it's also quite possible that the braking (damping) action is not sufficient to overcome the windmilling forces in this dive you're doing.

The short answer is to not dive to such a high speed. The complex answer, if this is not an option, is to arrange for some sort of mechanical lock from an extra channel. But just be sure to unlock before you start up or you'll let the smoke out, and that's bad.

For the prop to become unfolded, there has to be a motor-on glitch, after which the brake fails to engage. Chances are you are caught in the cross-fire between a receiver sending a brief motor-on glitch and a controller which then cannot re-engage its brake. Changing either component may solve the problem.
Question: does this happen at random, or only during certain maneuvers? If it's only during a dive, changing rx antenna routing may help.

Originally posted by ShredAir For the prop to become unfolded, there has to be a motor-on glitch, after which the brake fails to engage... http://shredair.com

As I have the same problem on my Jeti (old) "Gold" , and talked to Mr. Tinka (Jeti developer) about it in Aspach, I can confirm Dieter is right. The problem is that Jeti (unlike most of the other brushless controllers) only "brakes" for a short period after shutting down the motor. A glitch long enough to open the propeller blades , but too short to make the software realize the motor has come "on" then gives you a problem. A short "blip" of motor cures it. The solution to this would be a software upgrade. However, I've heard from different sources this did not help. The problem still being present with Hacker/Jeti controllers seems to confirm this. Another solution proposed by Mr Tinka was to use a PCM receiver. And I hear Mike Seale solved his problem by changing to a Schulze receiver.

So far I've had the problem 3 times in about 25-30 flights, once at high speed, twice during thermalling. I can live with it, but will try a Schulze receiver too.... (I hate PCM....)

I'm going to try a different RX and hope I get lucky.. I can't live with it.. If it happens in a dive again, I worry it'll tuck worse and might not recover. I don't want to switch all my stuff over to PCM, but I'd invest in a new FM rx if it cured the problem.. a shulze ESC is a little pricey, but when you look at the potential for losing everything, it might be a wise investment. Still if it's the radio glitching, I can't blame the hacker ESC

As an aside, the Multiplex IPD receivers are pretty much immune from glitching ... they act like a PCM (even with a programmable failsafe position for each channel), but from a normal transmitter. I fitted a 7 ch 'micro' IPD rx to a model that was suffering from intermittent glitching that I just couldn't cure (Jeti REX 7 rx), and got an instant fix.

Originally posted by tic Still if it's the radio glitching, I can't blame the hacker ESC

Interesting... Jeti, unable to fix its documented problem, convinces users to blame other components. Most receivers will glitch occasionally, often unnoticed. What if another receiver won't help? A new transmitter? A different plane?

Tic, before you give up and go back to Bandits and Zagis, see if you can move the receiver farther back and away from the flight battery and let the receiver antenna hang out the tail end; depending on how you're set up now, you may have to make up some extensions for the aileron servos.

Update; Sidemounted rx instead of flat on fuse floor, thinking a hairline crack in a circuit board might be causing a lost contact during high G flying, also rx mounted further back in fuse. As much antenna as possible coming out the back now.. Prop change to RF 15x13.... 4 flights yesterday, prop never came unfolded!.. LOT'S of highspeed dives, however on a slow pass at 100' or so, I saw the prop rotated a half a turn or so, not enough to unfold the blades , but I know I'm still getting the motor on glitch.. maybe the RF prop likes to stay folded better?... Next step will be to route antenna outside the fuse.. However, it's almost acceptable as is right now, as long as the prop stays folded, I'm happy. Strange I've never had glitching problems with any other hacker and hitec combo though.

Tic,
Sounds like you're making progress. I don't think the type of blades are relevant. The key will be eliminating the glitching that is the root cause.
If you're using an Airtronics or JR transmitter, you might try one of the blue Airtronics 777 receivers. I've found these to be more resistant to glitching in difficult environments.

The blade weight may be a factor, for example if the blades happen to fold above and below the fuse, then (especially a weighty Aeronaut cam 16x10 may droop the lower blade. The rf blades are in general much lighter. If they fold to the sides of the fuse, there is less of a problem.

I often use a small rubber band to help keep the blades together, with rf or HM lite spinners you can get a really close fit so that the rubber band cannot escape. The rubber seals used on electric toothbrushes make the best long lasting bands for this application.